According to the hot working technology, the calculating formulas of the end-roll strength in the automobile cross-beam steel have been given in theory with electron structure parameters of the alloying phase and the biphase interface. The relationships among the chemical composition, the end-roll grain size and the strength, achieved by calculations, are applied to predetermine the optimal end-roll grain size and chemical composition range to satisfy the technical requirements. In the productive process, according to the on-the-spot result analyzed, the computer can calculate the value of end-roll strength quickly, and the on-the-spot composition can also be adjusted in accordance with the demand until the composition is up to the technical requirements. The forecast is fit for all the non-quenched-tempered steels.